NSF/EAR-BSF: Resolving slow slip transients before and after the 2011 Tohoku-oki earthquake with geodesy and seismicity

构造板块运动在收敛的板块边界产生应力积累，并通过断层上的滑动释放。一些断层在地震中快速滑动，产生传统上由地震学家分析的波浪。其他断层滑动的速度要慢得多，而且没有地震，不会产生波浪。断层以长达几周的长期构造加载速率约100倍的速度滑动的事件通常被称为慢滑事件(SSE)。SSE通常伴随着微弱的地震活动，分析它们需要敏感的大地测量和地震台网的数据。SSE被认为在破坏性地震的启动中发挥了重要作用，因此阐明控制它们行为的物理因素是很重要的。大地测量仪器的进步使人们能够在几次大地震之前探测到SSE，其中2011年3月11日东北9.0级地震是历史上记录最好的地震。日本东北部时空地震大地测量网络的复盖范围为研究导致这场大地震及其后果的复杂活动提供了一个独特的机会。到目前为止，报告的前兆观测非常多样化，从GPS观测到的十年滑动加速到主震前两天的最终前震序列。该项目将对东北大地震前几十年的地震和无地震滑动相互作用进行更精确的描绘。该项目的研究人员开发了一种创新的方法，能够利用大地测量和地震活动数据检测低幅度SSE。这项研究的结果将为改进所有汇聚板块边界的短期地震危险评估工作提供参考。这个项目是与日本的研究人员和以色列特拉维夫大学的一名新教员通过两国NSF-BSF计划进行的国际合作。该项目旨在分析2011年3月11日东北9.0级大地震之前和之后几十年的无地震瞬时滑动的细节。通过使用大地测量匹配滤波技术，我们试图在大地测量时间序列中检测到比以前发展的技术所观测到的更低幅度的瞬变事件。研究人员将使用现有的和新的方法来同时分析大地测量和地震学观测，因为它们可能会提供关于常见物理现象的补充信息。该方法将首先应用于南开海槽，那里已经描述了许多慢滑事件，作为一种校准，并作为一种将GPS和倾斜仪数据结合在一种新的探测技术中的实验。其次，他们将在东北地区寻找短暂活动，重点是三陆近海和博索半岛下的两个地区。在三陆近海，反复发生的地震显示出滑动速率的振荡，大地测量仍需捕捉到这种振荡，以确定其空间和时间范围。在博索半岛下面，一系列具有重复间隔的慢滑事件正在进行，受到东北地震的干扰，地震活动和大地测量记录将被整合，以检测较低幅度的瞬时信号，并提高现有滑动模型的分辨率。主要目标将是解决东北地震应力扰动对慢滑事件的周期和动力学的影响。最后，研究人员将在日本东北部的尺度上开发导致东北9.0级地震的地震和无震级联事件的综合模型。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Tectonic plate motions produce stress accumulation at convergent plate boundaries, which is released by slip on faults. Some faults slip rapidly during earthquakes, generating waves, traditionally analyzed by seismologists. Other faults slip at much slower rates and aseismically, without generating waves. An episode during which the fault slips at rates that are about 100 times the long-term tectonic loading rate for periods of up to several weeks is commonly referred to as a slow slip event (SSE). SSEs are often accompanied by weak seismic activity and analyzing them requires data from sensitive geodetic and seismic networks. SSEs are thought to play an important role in the initiation of damaging earthquakes, and it is therefore important to elucidate the physics that controls their behavior. Advances in geodetic instrumentation have enabled the detection of SSEs occurring before several large earthquakes, among which the March 11, 2011 M9.0 Tohoku-oki earthquake is the best-recorded event in history. The spatiotemporal seismo-geodetic network coverage of northeast Japan provides a unique opportunity to study the complex activity leading up to this megathrust earthquake and in its aftermath. Precursory observations reported thus far are very diverse, ranging from a decadal slip acceleration observed by GPS to a final foreshock sequence two days before the main shock. This project will develop a more precise picture of seismic and aseismic slip interactions in the decades before the Tohoku-oki earthquake. The researchers on this project have developed an innovative method which enables the detection of low-amplitude SSEs using geodetic and seismicity data. The results from this research will inform efforts to improve short-term earthquake hazard assessments in all convergent plate boundaries. This project is an international collaboration with researchers in Japan and with a new faculty member at the Tel Aviv University in Israel, through the binational NSF-BSF program. This project aims to analyze the details of aseismic transient slip in the decades leading up to, as well as following the great March 11, 2011 M9.0 Tohoku-oki megathrust earthquake. By using a geodetic matched filter technique, we seek to detect lower-amplitude transient events in geodetic time series than the ones observed with previously developed techniques. The researchers will use existing and new methods to simultaneously analyze geodetic and seismological observations, as they are likely to provide complementary information about a common physical phenomenon. The methodology will be applied first to the Nankai trough, where many slow slip events have already been described, as a calibration and as an experimentation in combining GPS and tilt-meter data in a novel detection technique. Secondly, they will search for transient activities in the Tohoku area, with a focus on two areas, offshore Sanriku and beneath the Boso Peninsula. Offshore Sanriku, repeating earthquakes have shown oscillations in slip rates that still have to be captured by geodetic observation to determine their spatial and temporal extent. Beneath the Boso Peninsula, where a sequence of slow slip events with recurrence intervals disturbed by the Tohoku-oki earthquake is going on, seismicity and geodetic recordings will be integrated to detect lower-amplitude transient signals and to improve the resolution of existing slip models. A primary goal will be to resolve the impact of the Tohoku earthquake stress perturbation on the cycle and dynamics of the slow slip events. Finally, the researchers will develop a comprehensive model at the scale of northeast Japan of the seismic and aseismic cascade of events leading up to the M9.0 Tohoku-oki earthquake.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.